import math
x,y,a,b=map(float, raw_input().split())
print math.sqrt((a-x)**2+(b-y)**2) import math math x,y,a,b=map(float, raw_input().split()) x map(float, raw_input().split()) map float raw_input().split() ().split () raw_input split y a b print math.sqrt((a-x)**2+(b-y)**2) math.sqrt math sqrt (a-x)**2+(b-y)**2 (a-x)**2 a-x a x 2 (b-y)**2 b-y b y 2 y,a,b=map(float, raw_input().split()) map(float, raw_input().split()) y x,y,a,b=map(float, raw_input().split()) map(float, raw_input().split()) x a,b=map(float, raw_input().split()) map(float, raw_input().split()) a b=map(float, raw_input().split()) map(float, raw_input().split()) b
import math
x,y,a,b=map(float, raw_input().split())
print math.sqrt((a-x)**2+(b-y)**2)